Elasticity reconstructive imaging by means of stimulated echo MRI

Abstract

A method is introduced to measure internal mechanical displacement and strain by means of MRI. Such measurements are needed to reconstruct an image of the elastic Young's modulus. A stimulated echo acquisition sequence with additional gradient pulses encodes internal displacements in response to an externally applied differential deformation. The sequence provides an accurate measure of static displacement by limiting the mechanical transitions to the mixing period of the simulated echo. Elasticity reconstruction involves definition of a region of interest having uniform Young's modulus along its boundary and subsequent solution of the discretized elasticity equilibrium equations. Data acquisition and reconstruction were performed on a urethane rubber phantom of known elastic properties and an ex vivo canine kidney phantom using<2% differential deformation. Regional elastic properties are well represented on Young's modulus images. The long-term objective of this work is to provide a means for remote palpation and elasticity quantitation in deep tissues otherwise inaccessible to manual palpation.

Magnetic resonance elastography of the brain

“…Abnormal tissues commonly display a shear modulus up to 100 times that of normal tissue (Duck 1990;Sarvazyan et al 1994). These observations have prompted the development of techniques to quantitatively image the elastic modulus of various normal and abnormal tissues (Bishop et al 1998;Chenevert et al 1998;Fowlkes et al 1995;Lewa et al 1995;Muthupillai et al 1995;Ophir et al 1991;Parker et al 1990;Parker et al 1992;Plewes et al 1995;Van Houten et al 1999). Conventional imaging modalities such as radiography, computed tomography (CT), ultrasound (US), and magnetic resonance imaging (MRI) are not capable of directly assessing the mechanical properties of tissue.…”

Three‐dimensional subzone‐based reconstruction algorithm for MR elastography

“…[3] is facilitated by the expansion of the approximate displacement solution onto the basis set , so that:…”

“…As of yet, no direct correlation has been found between mechanical property contrast and a molecular contrast immediately discernible through standard MR imaging sequences. This necessitates the development of indirect imaging processes, most commonly algorithms which operate on the displacement or strain images that can be detected directly through MR phenomenon (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14). The reconstructive nature of these methods renders them sensitive to the accuracy with which they can account for behavior observed in the imaged data; that is, the final elastographic image produced by such indirect imaging algorithms can only be as good as the fundamental assumptions which underlie the reconstruction approach.…”

Application of DENSE‐MR‐elastography to the human heart

“…DENSE has been also proven as a reliable tool for encoding static displacements within phantom and ex vivo canine kidney (25). Here, we propose to use a DENSE sequence in combination with a steady-state sinusoidal mechanical excitation such that the encoding part of the DENSE sequence is synchronized to the frequency of the external vibration.…”